Servo-controlled magnetic valve

ABSTRACT

A servo-controlled magnetic valve has a main valve ( 13 ) and a servo valve ( 14 ). The servo valve opens when, after an empty stroke, a solenoid plunger ( 7 ) entrains a slide member ( 23 ) that carries the servo closure member ( 20 ) and, as a result, pressure is released to the low pressure side ( 17 ) from a pressure chamber ( 25 ) on the side of the servo piston ( 24 ) that is remote from the main valve seat ( 15 ). The servo piston ( 24 ) is an annular piston that surrounds an insert ( 19 ) that carries the main valve closure member ( 18 ) and the servo valve seat ( 20 ) and which, during the operating stroke, entrains the slide member ( 23 ) by means of first stops ( 26 ) and the insert ( 19 ) by means of second stops ( 28 ). In that manner, it is possible to obtain sufficient opening of the main valve ( 13 ) and a small overall height of the magnetic valve while retaining an initial empty stroke of the solenoid plunger ( 7 ).

The invention relates to a servo-controlled magnetic valve having a mainvalve, the main closure member of which can be raised from the mainvalve seat, which is fixed relative to the housing, by the operatingstroke of a servo piston, and having a servo valve, the servo closuremember of which can be raised from the servo valve seat when, after anempty stroke, a solenoid plunger entrains a slide member that carriesthe servo closure member and, as a result, pressure is released to thelow pressure side from a pressure chamber on the side of the servopiston that is remote from the main valve seat.

In a known magnetic valve of that type, the slide member consists of arod that carries the servo closure member at one end and a stop at theother end and, between them, carries a second stop. Arranged between thetwo stops is the solenoid plunger having corresponding counter-stops.During a first section of the operating stroke of the solenoid plunger,the plunger is accelerated without load so that, after an empty stroke,it comes into contact with the slide member with considerable energy.Since, simultaneously, the magnetic force has also increased, relativelysmall electromagnetic systems are sufficient to actuate the magneticvalve. After the empty stroke there follows a second section of theoperating stroke in which the slide member is removed from the region ofthe main valve seat so that the main closure member, which is provided,together with the servo valve seat, at the base of a pot-shaped servopiston, can open wide enough. This results in a relatively largeoperating stroke of the solenoid plunger and thus a large overall heightof the magnetic valve.

The problem underlying the invention is to provide a magnetic valvethat, under conditions that are otherwise the same, makes possible arelatively small overall height combined with a relatively large openingstroke of the main valve.

The problem is solved according to the invention in that the servopiston is an annular piston that surrounds an insert that carries themain valve closure member and the servo valve seat and which, during theoperating stroke, entrains the slide member by means of first stops andthe insert by means of second stops.

In that construction, after the solenoid plunger has executed the emptystroke, the slide member is no longer drawn outwards by the solenoidplunger, but is pushed outwards by the servo piston, the slide membercarrying out a stroke relative to the solenoid plunger in the oppositedirection to the empty stroke. Since the slide member does not need toproject out of the free end of the solenoid plunger, the desired smalloverall height is possible.

During its operating stroke, the servo piston also entrains the insertthat carries the main closure member, resulting in a large opening ofthe main valve. The entrainment of the insert, which is delayed relativeto the slide member, ensures that the servo valve remains open duringthe opening stroke of the main closure member and thus the openingaction is not interrupted. The empty stroke path of the solenoidplunger, the second stop and a step on the insert are so adapted to oneanother that the servo valve cannot close. Overall, a relatively largedegree of valve opening can be obtained with a very low differentialpressure for opening.

It is recommended that the first stops be formed by the annular end faceof the servo piston and co-operate with stop faces of the slide memberthat project radially beyond the insert, and/or that the second stops beformed by an inner flange of the servo piston and co-operate with anouter step on the insert. Such constructions can be manufactured veryeasily.

In a preferred embodiment, the slide member is generally in the shape ofa pot having a base plate and a pot wall, the adjacent end of theplunger piston engages inside the pot and relative movement is limitedby stops on the pot and on the plunger piston to the size of the emptystroke. This results in coupling between the slide member and plungerpiston that lends itself to the short overall height.

It is advantageous for the base plate to carry the servo closure memberin its centre and to project outwards beyond the diameter of the pot.The projecting portion forms the desired stop faces without the diameterof the pot having to be substantially larger than the diameter of thesolenoid plunger.

It is also advantageous for the pot wall to have a cut-away portion,through which the solenoid plunger can be inserted transversely to thestroke direction. In that manner, assembly can be simplifiedsubstantially.

It is advantageous for the base plate to have notches at its edge and/orholes that are located further in. In that manner, channels are producedthrough which fluid can, during movement of the slide member, passwithout a large throttling action, so that the movement of the slidemember is not hindered. This ensures that the fluid in the pressurechamber can flow out of the slide member when the valve is fully opened,which would not otherwise be able to take place because of the positionof the servo piston resting against the slide member.

It is recommended that the operating stroke of the solenoid plunger beonly slightly larger than the empty stroke. An extremely small overallheight is thus obtained.

Preferably, in addition to a closing spring that acts upon the solenoidplunger, a relatively weak pressure spring is provided between the slidemember and the solenoid plunger. That pressure spring prevents thesolenoid plunger from “sticking” to the slide member and hence stops theservo valve from opening before the empty stroke has been completed.

Moreover, in addition to a closing spring that acts upon the solenoidplunger, it is advantageous for a relatively weak pressure spring thatacts in the direction of the operating stroke to be provided between thehousing and the servo piston. That pressure spring ensures that theservo piston starts its operating stroke as soon as the servo valve isopen. In the limit, the differential pressure for opening can be reducedto zero.

The invention is described hereinafter in greater detail with referenceto preferred embodiments shown in the drawings, in which:

FIG. 1 is a section through a magnetic valve according to the inventionin the closed state;

FIG. 2 shows the magnetic valve of FIG. 1 in the open state;

FIG. 3 is a perspective view of a slide member that can be usedaccording to the invention; and

FIG. 4 is a modified construction.

The magnetic valve shown has an electromagnet 1 having a coil 2 which iswound on a coil former 3 and is surrounded by a yoke 4. A tubulararmature 5, into the outer end of which there is introduced a plug 6made of a magnetically conducting material, is held by the coil former3. Also provided in the tubular armature 5 is a solenoid plunger 7 whichis acted upon by a closing spring 9 that is received in a blind bore 8.The electromagnet 1 is connected fixedly to a valve housing 10 by way ofthe tubular armature 5. For that purpose, the tubular armature 5 has atits lower end a radially angled collar 11 which is held in place on thevalve housing 10 by means of a flange-like clamping piece 12, forexample, by screws.

Located in the valve housing 10 are a main valve 13 and a servo valve14. The main valve 13 has a main valve seat 15, which is fixed relativeto the housing and which is arranged between the inlet-side pressureside 16 and the outlet-side low pressure side 17, and a main closuremember 18 which is provided on the underside of an insert 19. The servovalve 14 has a servo valve seat 20 which is located on the upper side ofthe insert 19 and which forms the inlet to a channel 21 that leads tothe low pressure side 17, and a servo closure member 22 which isprovided on the underside of a slide member 23.

The insert 19 is surrounded by a servo piston 24, which, on its end facethat is remote from the main valve seat 15, bounds a pressure chamber 25which, when the main and servo valves are shut, carries the inlet-sidepressure by virtue of leakage channels and, when the servo valve 14 isopened, carries the outlet-side low pressure. On its upper end face, theservo piston 24 has first stops 26 which co-operate with stop faces 27on the underside of the slide member 23 and, on an inner flange of theservo piston 24, second stops 28 which co-operate with an outer step 29on the insert 19. The distance between the first stops 26 and theassociated stop faces 27 is smaller than the distance between the secondstop faces 28 and the associated step 29. This means that, when theservo piston 24 is moved, first the slide member 23 and then the insert19 are entrained, the entrainment movement accordingly taking place whenthe servo valve 14 is open. The ratio of the diameters of the servopiston 24 and the insert 19 is so selected that the main valve can openand is typically approximately 2:1.

The slide member 23 has a substantially smaller axial length than thesolenoid plunger 7. It is substantially in the shape of a pot having apot wall 30 and a base plate 31. The diameter of the pot is slightlysmaller than the diameter of the solenoid plunger 7. The base plate 31projects beyond the diameter of the pot in order to form the stop faces27. An armature foot 32 projects inside the pot and, at the lower end,has a double stop 33 which, in one end position, co-operates with a stop34 that is formed by the upper side of the base plate 31 and, in theother end position, co-operates with a stop 35 that is formed by aninner flange of the slide member 23. The slide member 23 and thesolenoid plunger 7 can thus be moved relative to one another in an emptystroke S. That empty stroke S is slightly smaller than the operatingstroke L that can be covered by the solenoid plunger 7.

Further details of the slide member 23 can be found in FIG. 3. The potwall 30 has an opening 36 so that the armature foot 32 can be insertedinside the pot transversely to the stroke direction, despite thepresence of the double stop 33. The base plate 31 also has notches 37 onthe outside and, located further in, holes 38 which enable fluid to passunthrottled from the underside to the upper side of the base plate 31and vice versa, which means that the operation of the magnetic valve isnot hindered by throttle resistances.

The magnetic valve operates as follows:

1. When the main valve 13 is closed (FIG. 1) and the electromagneticvalve 1 is excited, the solenoid plunger 7 executes its operating strokeL. In so doing, the double stop 33, after a no-load empty stroke S,comes into contact with the stop 35 of the slide member 23 and entrainsthe latter for a short distance. As a result, the servo valve 14 opensand pressure is released from the pressure chamber 25 to the lowpressure side 17 via the channel 21. The force exerted on the servopiston 24 from below by the fluid pressure then prevails so that theservo piston 24 is displaced upwards and in so doing entrains first theslide member 23 by means of its first stops 26 and then the insert 19 bymeans of its second stops 28. This means that, with the servo valve 14remaining open, the slide member is pushed upwards in a strokecorresponding to the empty stroke S. The insert 19 also carries out thatmovement so that the main valve 13 is opened and the cross-section ofthe opening is large. That state, shown in FIG. 2, is maintained as longas the electromagnet is excited.

2. When the exciting current is interrupted, the closing spring 9ensures that the solenoid plunger 7 is pushed downwards, so that,following a short movement, the armature comes to rest on the base ofthe slide member 23 and closes the holes 38. Because the double stop 33is resting against the stop 34, the armature entrains the slide member23, as a result of which the servo valve 14 closes. The inlet-sidepressure builds up again in the pressure chamber 25 via leakagechannels, as a result of which the servo piston 24 and the insert 19return to the resting position shown. The main valve 13 closes at firstslowly and then more and more rapidly until the position in FIG. 1 hasbeen reached. When the insert 19 comes to rest against the main valveseat 15, the main valve remains closed but the servo valve is still openuntil the further movement of the slide member finally causes the servoclosure member 22 to come to rest against the servo valve seat 20.

The construction of FIG. 4 corresponds to that of FIGS. 1 to 3, exceptthat two springs are present in addition to the closing spring 9. Theseare: a first pressure spring 39, which is weaker than the closing spring9 and is connected between the solenoid plunger 7 and the slide member23 and ensures that there is reliable separation from the slide member23 at the start of the empty stroke of the solenoid plunger 7; and asecond pressure spring 40, which is weaker than the closing spring 9 andis arranged between the valve housing 1 and the servo piston 24. Thatspring is able to raise the servo piston 24 until it rests against theinsert 19 and ensures that even small pressure differentials aresufficient to make the servo piston 24 move and thus to open the mainvalve 13. Moreover, with suitable dimensioning, it is also possible toobtain a braked closing movement with that pressure spring 40.

It is possible to diverge from the embodiments shown, in many respects,without departing from the basic concept of the invention. For example,instead of engaging over the armature foot 32, it is also possible forthe slide member to engage, by means of a central continuation piece, ina corresponding opening of the solenoid plunger 7. The movement of thesolenoid plunger 7 is favourably influenced if the upper and lower endfaces are connected to one another, for example by an extension of theblind bore 8 by a bore of relatively small diameter.

What is claimed is:
 1. Servo-controlled magnetic valve having a mainvalve with a main closure member which can be raised from a main valveseat by an operating stroke of a servo piston, the main valve seat beingfixed relative to the housing, and having a servo valve with a servoclosure member which can be raised from the servo valve seat when, afteran empty stroke, a solenoid plunger entrains a slide member that carriesthe servo closure member and, as a result, releases pressure to a lowpressure side from a pressure chamber on a side of the servo piston thatis remote from the main valve seat, the servo piston being an annularpiston that surrounds an insert that carries the main valve closuremember and the servo valve seat and which, during the operating stroke,entrains the slide member by means of first stops and the insert bymeans of second stops.
 2. Magnetic valve according to claim 1, in whichthe first stops are formed by an annular end face of the servo pistonand co-operate with stop faces of the slide member that project radiallybeyond the insert.
 3. Magnetic valve according to claim 1, in which thesecond stops are formed by an inner flange of the servo piston andco-operate with an outer step on the insert.
 4. Magnetic valve accordingto claims 1, in which the slide member is generally in the shape of apot having a base plate and a pot wall, an adjacent end of the plungerpiston being engaged inside the pot and relative movement being limitedby stops on the pot and on the plunger piston to an empty stroke. 5.Magnetic valve according to claim 4, in which the servo closure memberis located at a center of the base plate and projects outwards beyondthe pot.
 6. Magnetic valve according to claim 4, in which the pot wallhas a cut-away portion through which the solenoid plunger can beinserted transversely to stroke direction.
 7. Magnetic valve accordingto claim 4, in which the base plate has at least one of notches at itsedge and holes located further in from the edge.
 8. Magnetic valveaccording to claim 1, in which the solenoid plunger has an operatingstroke which is only slightly larger than the empty stroke.
 9. Magneticvalve according to claim 1, in which, in addition to a closing springthat acts upon the solenoid plunger, a relatively weak pressure springis provided between the slide member and the solenoid plunger. 10.Magnetic valve according to of claim 1, in which, in addition to aclosing spring that acts upon the solenoid plunger, a relatively weakpressure spring that acts in the direction of the operating stroke isprovided between the housing and the servo piston.